1. Field of the Invention
This invention relates to an apparatus for measuring ionic activity of electrolytes contained in aqueous liquid samples such as body fluids. More particularly, this invention relates to a novel potentiometric electrolyte analyzer in which a slide-type ionic activity measuring device having ion-selective electrodes is transferred from a spotting section to a discharging section by way of a measuring section.
2. Description of the Prior Art
Measurement of ionic activity of an electrolyte ion, for example Na.sup.+, K.sup.+, Cl.sup.-, Ca.sup.2+, HCO.sub.3.sup.- or CO.sub.3.sup.2-, contained in such body fluids as whole blood, blood plasma, blood serum, and urine, has significant importance in clinical chemistry tests. For this measurement, an ionic activity measuring apparatus, i.e. a so-called electrolyte analyzer, has been used. Such techniques as flame analysis, coulometry and potentiometry are known for use in said analyzer.
In potentiometric measurement of ionic activity, an ionic activity measuring device having ion-selective electrodes is used. As such a device, a dry type device having film-like ion-selective electrodes has been disclosed, for example, in U.S. Pat. Nos. 4,053,381 and 4,437,970.
The basic structure of this ionic activity measuring device is that of a slide comprising at least one pair of solid state electrodes each of which has an ion-selective outermost layer and a porous bridge which can promote capillary action between two such ion-selective layers. The ionic activity of a specific ion contained in a sample solution can be determined by spotting a reference solution on one of the ion-selective layers and a sample solution on the other and then measuring the potential difference between the electrodes.
Accordingly, spotting of reference and sample solutions as well as measurement of potential difference must be conducted in an ionic activity analyzer in which this slide type device is used.
The conventional analyzer for this purpose is not only large in size but also has the following drawbacks in the structure of the means for spotting the reference solution. In the conventional analyzer since the reference solution is pumped up from reservoir by a nozzle and then spotted on the slide by the same nozzle, the surface of the reference solution comes into contact with air, causing a change in the concentration thereof. Also, since the nozzle has to be sufficiently deep into the solution so it is not exposed by a lowering of the liquid level, the volume of liquid which adheres to the wall of the nozzle on suction changes at each suction so that the spotting volume is not constant.
In such measurement of the ionic activity, the change in concentration of the solution, which causes errors in the measurement, becomes a particularly serious problem in practice.